Low pressure mercury vapor discharge lamps including an alloy type getter coating



United States Patent Akira Hama Himeji-shi;

Tadaaki Watanabe, Hyogo-ken, 0; Shunji Kikuchi; Norio Kumagai, Yokohama-shi,

Inventors Japan Appl. No. 733,706 Filed May 31,1968 Patented Dec. 22, 1970 Assignee Tokyo Shibaura Electric Co. Ltd. Kawasaki-shi, Japan a corporation of Japan Priority June 3, 1967 Japan No. 42/46877 LOW PRESSURE MERCURY VAPOR DISCHARGE LAMPS INCLUDING AN ALLOY TYPE GETTER COATING 11 Claims, 3 Drawing Figs.

US Cl 313/178, 313/109, 313/179, 313/185 Int. Cl ..H0lj 61/20, H01j 6l/26,H01j 61/35 Field of Search 313/ 109,

178, 179,185,176, 107, 21 l, (Cursory); 252/1816; 117/221 [56] References Cited UNITED STATES PATENTS 2,444,423 7/1948 Braunsdorff 313/178 2,491,284 12/1949 Sears 313/178X 2,692,347 10/1954 Mason 313/109 2,748,306 5/1956 Bjorkman 313/178X 2,769,112 10/1956 Heine et al 313/109X 2,855,368 10/1958 Perdijk et al..... 252/18l.6 2,885,587 5/1959 Wainio et al..... 313/109X 2,939,985 6/1960 Kolkman 313/185 2,959,702 11/1960 Beese 313/109 3,264,510 8/1966 Griffiths 3l3/178X 3,308,329 3/1967 Foreman et al 313/107 Primary Examiner-James W. Lawrence Assistant Examiner-Palmer C. Demeo Attorney-George B. Oujevolk ABSTRACT: A low-pressure mercury vapor discharge lamp wherein a pair of electrode mounts are sealed to the ends of the light-transmissive elongated sealed envelope having a getter of titanium-nickel alloys containing more than 5 percent by weight of titanium, The getter effectively adsorbs free oxygen released in the discharge lamp thereby greatly restricting the possible formation of end bands or end blackenings on the inner wall of the envelope in the vicinity of the electrode.

LOW PRESSURE MERCURY VAIOR DISCHARGE LAMPS INCLUDING AN ALLOY TYPE GIE'I'IER COATING The present invention relates to a low pressure mercury vapor discharge lamp and more particularly to a low pressure mercury vapor discharge lamp such as a fluorescent lamp containing a pair of electrodes.

In a low pressure mercury vapor discharge lamp, for example a fluorescent lamp, there appears in the vicinity of each electrode a ringlike blackening known as an end band, before the life of the lamp is used up. This end band degrades the appearance of the lamp and reduces the luminous output thereof. The occurrence of the end band is generally deemed to originate with the fact that materials for activating the cathode coated on each electrode, vitreous elongated sealed envelope such as a glass tube itself and fluorescent materials applied on the inner wall of said envelope release oxygen during the operation of the lamp, the oxygen thus released reacts with the mercury filled in the envelope to form black mercury oxides and these products are deposited on that part of the inner wall of the glass tube which is disposed adjacent to the Faradays dark space having a small potential gradient. Therefore the generation of such end bands will be avoided by trapping free oxygen present in the envelope. To adsorb gases remaining in the envelope before sealing a common discharge lamp, it is generally the practice to use substances capable of adsorbing such gases, namely, getters. We have found, however, that ordinary getters which consist of active metal such as titanium adsorb the gases in normal operating temperature, thus the end bands are not produced, but nonringlike blackenings known as anode spots are still produced whereby the utility of the lamp will be reduced.

The present invention provides a low pressure mercury vapor discharge lamp comprising a light-transmissive elongated sealed envelope containing a filling of mercury and starting rare gas at a pressure of a few millimeters of Hg, a pair of electrode mounts sealed at both ends of said envelope and supporting a filament coated with activated electron-emitting materials, and a getter disposed on the portion of said mounts except the activated electron-emitting materials coated portion of said mounts, which consists of titanium-nickel alloy containing more than percent by weight of titanium.

In a low pressure mercury vapor discharge lamp according to the present invention, the gases, particularly oxygen, released from the inner wall of the envelope, the fluorescent material and the activated electron-emitting materials are readily adsorbed by the aforesaid getter material having a moderately suppressed gettering action for a long period of time, before these gases can react with the mercury or vapor thereof present in the lamp to form black mercury oxides. Therefore, this discharge lamp is prevented from presenting the aforementioned end bands during its expected long life.

The present invention can be more fully understood by the following description taken in connection with the accompanying drawings in which:

FIG. I is a cross section of a part of a low pressure mercury vapor discharge lamp according to the present invention, with a part of the envelope broken away to show an electrode mount;

FIG. 2 is a perspective view of the flared stem used in another embodiment of the invention; and

FIG. 3 is a perspective view of the flared stem used in a further embodiment of the invention.

Referring to the drawings, more particularly to FIG. I, the low pressure mercury vapor discharge lamp of this invention comprises a cylindrical glass envelope 1 having fluorescent materials coated on the inner wall thereof and a pair of electrode mounts 2 (this FIG. indicates only one of them) sealed to both ends of the envelope l in a manner to close them. Since these mounts are of substantially the same construction, only one of them will hereinafter be described. The electrode mount 2 consists of a flared glass stem 3 hermetically sealed to the envelope, which has a pair of inner-lead wires of lead-in wires 5 and 6, the wires supporting a filament 7 which is coated with activated electron-emitting materials such as Ball- Srtl-(Iat) containing M znn. A base shell 8 which has a pair of base pins 9 and 10 is fitted with proper cement II to the outer side of the stem 3. The lead-in wires 5 and 6 are connected to the pins 9 and 10, respectively.

At suitable parts on the surfaces of the lead-in wires 5 and 6 there are formed getters 112 and 13. The getter consists of titanium-nickel alloys containing more than 5 percent by weight of titanium. The getter may be formed on the surface of the filament supporting lead-in wires and/or at other appropriate parts in the vicinity of the filament 7, for example on the surface of the flared stem 3. The getter may be composed of powders of titanium-nickel alloys containing more than 5 percent by weight of titanium. A preferable method of forming a getter consists in mixing powders" of titanium-nickel alloys with a suitable binder, coating the: mixture on a suitable part of the lead-in wires or other parts of the mounts and heating the alloy powders by means of flow of current to the leadin wires.

In FIG. 2, there is illustrated another electrode mount used in the mercury vapor discharge lamp of this invention. The mount includes a flared glass stem 20, and a pair of lead-in wires 21 and 22 which extend to base pins (not shown) secured to a base shell through the stem 20 and support a fila ment 23 coated with activated electron-emitting materials on the surface thereof. The lead-in wires have wire anodes 24- and 25, respectively, in a parallel arrangement, on which getters 2.6 and 27 are formed.

A further electrode mount is shown in FIG. 3 wherein a flared stem 30 has a pair of lead-in wires 31 and 32 which support a filament 33 coated with electron-emitting materials on the surface thereof. Around the filament 33 is arranged a shield electrode 34 which is supported by a support pin 35 planted on the stem 30. In this embodiment a getter 36 may be formed on the surface of the shield electrode.

It has been experimentally confirmed that a low pressure mercury vapor discharge lamp of the present invention, having a getter formed at a suitable part in the vicinity of the filament, the occurrence of end band is restricted to a far greater extent than in the prior art discharge lamp of the same specification. This is clear evidence that the getter action of the titanium-nickel alloy used in the discharge lamp of this invention effectively limits the generation of black mercury oxides from which the end bands result. Furthermore, although the mechanisms are not clearly understood, the occurrence of anode spots is considerably reduced. While it is not yet fully understood by what mechanisms the titanium-nickel alloy getter containing more than 5 percent by weight of titanium suppresses the production of black mercury oxides, this is believed to arise from the fact that under the condition of elevated temperatures when the discharge lamp is lit, the titanium-nickel alloy exhibits over a long period of time an action of adsorbing free oxygen present in the envelope. Thus, it is considered that when oxygen molecules contact the surface of this specific titanium-nickel alloy they are adsorbed to the surface at the contact point and slowly diffuse into the interior of the alloy with a lapse of time, and consequently always render the getter surface sufficiently activated to adsorb oxygen molecules. In contradistinction to this, ordinary getter materials, such as titanium, are unable to adsorb oxygen molecules at such elevated temperatures as prevailing in the glass tube when the discharge lamp is lit.

As previously mentioned, it is indispensable for the attainment of the object of the present invention that the titaniumnickel alloy constituting the getter layer should contain more than 5 percent by weight of titanium. It has been disclosed that if the titanium content is less than 5 percent by weight, the titanium-nickel alloy will decrease its capacity for adsorbing oxygen and not be effective in preventing in occurrence of end bands. Also, the getter layer may include in addition to the titanium-nickel alloy other common materials quite able to adsorb oxygen such as iron and/or aluminum.

, As described above, the discharge lamp of the present invention having a layer of titanium-nickel alloys containing more than 5 percent by weight of titanium fonned at an adequate part in the vicinity of the filament is effectively protected from the occurrence of end bands, so long as the lamp is maintained in a normal operating condition. Therefore during the normal operation, the present invention can unfailingly eliminate the degradation of appearance of the discharge lamp resulting from the generation of end bands or the decrease of the lamp life due to reduced luminous output. 7

While the invention has been described in connection with some preferred embodiments thereof, the invention is not limited thereto and includes any modifications and alterations which fall within the scope of the invention as defined in the appended claims.

We claim:

1. A low pressure mercury vapor discharge lamp comprising a light-transmissive sealed envelope containing a filling of mercury and starting rare gas at a pressure of a few millimeters Hg,a pair of electrode mounts sealed at both ends of said envelope and supporting a filament coated with activated electron-emitting materials, and a getter disposed on the portion of said mounts except the activated electron-emitting materials coated portion of said mounts, which consists of titaniumnicl'el alloy containing more than 5 percent by weight of titanium.

2. A low pressure mercury vapor discharge lamp according to claim 1 wherein the alloy of said getter further contains iron.

, 3. A low pressure mercury vapor discharge lamp according to claim 1 wherein the alloy of said getter further contains aluminum 4. A low pressure mercury discharge lamp according to claim 1 wherein the alloy of said getter further contains iron and aluminum.

5. A low pressure mercury vapor discharge lamp comprising a light tra'ns'riiis'sive elongated sealed envelope'containing a filling of mercuryand starting rare gas at a pressure of a few millimeters Hg, a pair of electrode mounts consisting of a stem sealed at the ends of said envelope, a pair of inner-lead wires sealed in'said stem so as to connect to the electric source. a filament supported between said inner-lead wires and "activated electron-emitting materials coated on said filament, and a getter disposed on'the portion of said mounts except the activated electron-emitting materials coated portion and consisting of titanium-nickel alloys'containing more than 5 percent by weight of titanium.

6. A low pressure mercury vapor discharge lamp according to claim 5 wherein said electrode mounts further include an auxiliary electrode disposed around said filament and connected to said inner-lead wires, and said getter is formed on the" surface of said auxiliary electrode.

7. A low pressure mercury vapor discharge lamp according to claim 5 wherein said electrode mounts further include a pair of anode electrodes disposed around said filament and connected to said inner-lead wires, and said getter is formed on the surface" of said anode electrodes.

8. A low pressure mercury vapor discharge lamp according to claim 5 wherein each of said electrode mounts further includes a shield surrounding said filament, and said getter is formed on said shield.

9. A low pressure mercury vapor discharge lamp according to claim 5 wherein said getter is formed on said inner-lead wires.

10. A low pressure mercury vapor discharge lamp according to claim 5 wherein said getter is formed on said filament except the portion coated with the activated electron-emitting materials.

11. A low pressure mercury vapor discharge lamp according to claim 5 wherein said getter is formed on the outer surface of said stem. 

